Fair Value Disclosure (Narrative) (Details) $ in Millions	Jun. 30, 2016 USD ($)
NBCUniversal Enterprise [Member]
Fair value of redeemable preferred stock	$ 761

Fair value of our redeemable subsidiary preferred shares and/or stock

No definition available.

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Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant